Method for locating sensors mounted each on a vehicle wheel

ABSTRACT

Each sensor is provided with an emitter and the vehicle is provided with a corresponding receiver adapted to receive signals emitted by each sensor. The receiver is provided with at least one antenna disposed such that it is not located substantially equidistantly from the sensors, the antennas being located on a same side of the vehicle. The location of the sensors is carried out by analyzing the power of the field received by the receiver of each antenna for each sensor, the field power received by one antenna being the greater, the nearer to the antenna is the sensor that emitted the corresponding signal.

The present invention relates to a process for locating a sensorassociated with a vehicle wheel. This process permits for exampledetermining the position (front, rear, right, left, . . . ) of apressure sensor mounted in an automotive vehicle tire.

In a vehicle provided with a system for surveillance of the pressure ofthe tires, it is necessary to be able automatically to identify thelocation of a pressure sensor. Thus, when information concerning thepressure of a tire is sent to a central unit, the latter must know towhich tire the received pressure information corresponds.

Information concerning tire pressure, in a tire pressure surveillancesystem, is sent from sensors located at the wheels toward the centralunit by radio waves. An antenna fixed relative to the chassis of thevehicle receives the information and transmits it. Certain pressuresurveillance systems for tires provide one antenna per wheel and henceper pressure sensor. In this case, the identification of the wheel takesplace by filtering. For a given antenna, the most powerful signalreceived corresponds to the pressure sensor nearest the antenna. Thelocation of the wheel and of the associated sensor thus takes place inthis way.

However, to simplify the systems and to render it more economical, it ispreferable to have but a single receiver. When a pressure sensor thusemits information, it must be possible to determine with which wheelthis sensor is associated. For an automotive vehicle comprising fourwheels, it is necessary to determine whether the sensor is associatedwith a front wheel or a rear wheel and also whether the informationcomes from a wheel located on the right or on the left of the vehicle.

The document FR 2 774 178 discloses a process for locating andrecognizing the position of the wheels on a vehicle. In this case, thewheels are provided each with a sensor emitting a detection signalrepresentative of a condition of the corresponding wheel. The vehicle isitself provided with a device for processing the detection signal. Theprocess described in this document consists in predetermining asignature of a detection signal emitted by a sensor carried by a wheel,and memorizing this signature and the corresponding position of thewheel in the processing device. The recognition of the position of awheel is obtained by analyzing the signature of a detection signal andby comparing this signature to the memorized signatures.

The present invention thus has for its object to provide a new processfor automatic location which permits indicating to which wheelcorresponds a signal received with a single receiver. This process canpreferably be practiced with means that are not very expensive.

To this end, it provides a process for locating sensors each mounted ona vehicle wheel, each sensor being provided with an emitter and thevehicle being provided with a corresponding receiver adapted to receivethe signals emitted by each sensor.

According to the invention, the receiver is provided with an antenna,disposed such that it is not substantially equidistant from any twosensors, and the location of the sensors is carried out by analyzing thepower of the field received by the receiver by means of the antenna foreach sensor, the field power received by the antenna being the greaterthe nearer to the antenna is the sensor that emitted the signal.

This location process is based on the physical principle known asattenuation of an electromagnetic field as a function of distance. Thisattenuation is proportional to the inverse of the square of thedistance. The process according to the invention uses this physicalprinciple. Thus, for a given antenna, the more powerful signal receivedcorresponds to the emitter, in this case associated each time with asensor, that is nearest, and the reception power decreases as a functionof the distance between the emitter and the receiver.

It is not necessary to know exactly the power of the received signal. Itsuffices to know the power relative to signals corresponding to thedifferent sensors. It is possible to estimate this power of theelectronic measurement with the help for example of a device forindicating power of the RSSI type (Receiver Signal Strength Indicator).A modification of this measurement could consist in causing thesensitivity of the receiver to vary. To the extent that this sensitivitydecreases, the number of signals received also decreases. One can thusdeduce the relative distance of the sensors, the more remote sensorsbeing those from which are no longer detected the initial signals.

To increase the reliability of the results obtained by this process, theinvention also proposes a process using at least two antennas. It is amatter of locating sensors each mounted on one wheel of the vehicle,each sensor being provided with an emitter and the vehicle beingprovided with a corresponding receiver adapted to receive the signalsemitted by each sensor. In this process, the receiver is provided withtwo separate antennas, separated from each other and disposed such thatno antenna is substantially equidistant from the sensors, the twoantennas being located on a same side of the vehicle, and the locationof the sensors being established by analyzing the power of the fieldreceived by the receiver by means of each antennas for each sensor, thefield power received by an antenna being the greater, the nearer thesensor emitting the corresponding signal is to the antenna.

For a vehicle comprising four wheels, this process according to theinvention comprises for example the following steps:

-   -   a) analysis of the power of the signals received by the two        antennas so as to distinguish the two sensors located on the        side of the antennas from two other sensors, the signal received        from these two sensors being the less attenuated,    -   b) one antenna being inactivated and the other being activated,        analysis of the power of the signals received from the two        sensors which are located on the same side as the antenna so as        to determine which sensor is nearer the antenna that is still        activated, and    -   c) one antenna being inactivated and the other activated,        analysis of the power of the signals received from the two        sensors that are located on the side opposite the antennas so as        to determine which sensor is the nearer the antenna that is        still activated.

It is necessary to break down the location process into severalsuccessive steps, permitting increasing the reliability of the obtainedresults.

Step a) of the above process is for example carried out as follows:

-   -   adjustment of the receiver to a predetermined sensitivity to        receive all the signals emitted by the four sensors with the two        antennas, and    -   adjustment of the receiver to a lesser sensitivity such that,        for the two antennas, the signals emitted by the sensors located        on the same side as the antennas will be received whilst the        signals emitted by the other sensors will not be received.

In this location process, in step b) and/or step c), the power analysisis for example carried out by adjusting the sensitivity of the receiversuch that the power of the signal received by the sensor to beidentified and located near the inactive antenna, will be weak whilstthe power of the signal received by the sensor to be identified andlocated near the active antenna will be substantially stronger. Thesensitivity of the receiver can thus be decreased until a single signalis received.

This signal thus corresponds to the signal emitted by the nearestsensor. It is thus possible to determine the position of the two sensorswhose signals are analyzed.

In the case of step b), the sensors to be identified are the sensorslocated on the side of the antennas whilst in the case of step c), thesensors to be identified are the sensors located on the opposite sidefrom the antennas.

In another embodiment of the process, in step b) and/or in step c), thepower analysis is for example carried out by decreasing the sensitivityof the receiver until but a single signal emitted by the sensors to beidentified will still be received by the receiver, and a deduction ofthe position of the two sensors to be identified is thus achieved.

In step c), the signals from all the sensors are of course received,including those located on the side of the antennas. However, thesesignals are already modified as being from the side of the antennas fromstep a) and we are thus interested only in signals received by the othersensors, which is to say those disposed on the side opposite to theantennas.

To increase the reliability of the location process described above,step b) and/or c) is preferably carried out twice in succession, oncewith a first antenna active and the second antenna inactive, and thesecond time with the first antenna inactive and the second antennaactive, and a correlation step is then provided to compare the resultsobtained in the course of these two analyses.

Similarly, again to increase the reliability of the process, step c) iscarried out several times in a repetitive manner and a statisticalanalysis of the results is made. This can be generalized for all theprocess (with one or several antennas) which is thus preferably carriedout in a repetitive manner and a statistical analysis of the resultsthus obtained is made.

In a modified embodiment, the two antennas are integrated into theinstrument panel of a vehicle, one antenna being located in the rightportion and the other in the left portion of this instrument panel. Inthis way, the two antennas will be located in the front of the vehicle,one to the right and the other to the left. In this modification, oneantenna can be integrated with an electronic housing integrating thereceiver, whilst the other antenna is for example an antenna external tothis housing.

The present invention also relates to a location device to practice aprocess such as described above, characterized in that it comprises areceiver, two antennas, a switch with two inlets insulated from eachother and an outlet, mounted such that the receiver is connected to oneor the other of the antennas, as well as a computer for controlling andmanaging the device.

In a modified embodiment of this device, the receiver is integrated intothe computer. It can also be provided that one antenna is integratedinto the computer and the other antenna is an external antenna.

The details and advantages of the invention will become betterunderstood from the description which follows, given with reference tothe accompanying schematic drawing, in which:

The single figure represents schematically a vehicle seen from above,provided with an automatic device for locating sensors according to theinvention.

The process according to the invention is adapted to be performed in anautomotive vehicle provided with four wheels, each of these wheels beingitself provided with one pressure sensor. In a manner known per se, eachpressure sensor includes an RF (Radio Frequency) emitter. The vehicle isitself provided with a corresponding receiver. In this way, themeasurements carried out by the pressure sensor can be transmitted to acomputer which analyzes and interprets the data it receives.Conventionally, the communication between the sensors and the receivertakes place with the help of a signal of 433 MHz.

The process according to the invention, described hereafter, permits thereceiver, where it receives a signal from a sensor, to know where thissensor is located and thus to determine with which wheel it mustassociated the information received. Thus, each sensor, when it emits asignal toward the receiver, sends a code identifying it as well as theinformation to be transmitted. However, because the wheels can berotated and changed as to position (right-left exchange of the tires orfront-rear exchange) the recognition of the code identifying the sensoris not sufficient to know where this sensor is located.

In a novel way, the process according to the invention proposes carryingout an automatic location of the pressure sensors mounted on the wheelsof the vehicle, by using the property of attenuation of the power of theelectromagnetic waves when they propagate.

The system used to practice this process is shown schematically in thesingle figure accompanying the present specification.

So that this system can operate, it is necessary that a vehicle 2,provided with four wheels 4 be provided, for each tire of the wheels 4,one sensor. Let it be supposed in what follows that it is here a matterof pressure sensors, but sensors could also be conceived of another typefor example a temperature sensor. The vehicle 2 is thus provided withfour sensors: one front left sensor indicated at 100, one front rightsensor indicated at 101, one left rear sensor indicated at 110 and aright rear sensor indicated at 111. As already indicated above, each ofthese sensors is provided with an RF emitter.

The vehicle 2 is itself provided with a single RF receiver 6 adapted toreceive signals emitted by the four sensors 100, 101, 110, 111. Thisreceiver 6 is indicated into a controllable computer 8. The signalsarriving at the receiver 6 are received by two antennas. A first antenna12 is an antenna integrated into the computer 8. It can for example bean antenna printed on a circuit of this computer. The second antenna isan external antenna 14 for example an antenna of the quarter wave type.A switch having two inputs and one output is integrated into thecomputer 8. It permits connecting the receiver 6 either to the internalantenna 12 or to the external antenna 14. The two inputs of this switchare insulated from each other with a minimum insulation of 30 dB. Thecontrol of the switch is ensured by the computer 8.

The receiver has a sensitivity adjustable by means of a gain controldevice. It also comprises an output of the RSSI type (Receiver SignalStrength Indicator). This output permits the analysis of the field levelreceived by the emitters associated with the sensors 100, 101, 110, 111.The gain control functions and analysis of the field level received, arealso managed by the computer 8 with the help of an analog/digital portfor the RSSI output and a logic port for the gain control.

Let it be supposed that four sensors 100, 101, 110, 111 are all fouridentical. As indicated above, the emitter associated with each of thesensors, when it emits an RF signal, first emits an identifying codecorresponding to each sensor. The identifying codes emitted by thesensors 100, 101, 110, 111 are recognized by the computer 8. Let it forexample be supposed that the identifying codes for these sensors arerespectively 100, 101, 110 and 111. The computer 8 recognizes thesecodes but does not know where the corresponding sensor is geographicallylocated. All the sensors being identical, it can thus be supposed thatthe power emitted by each of these sensors is substantially the sameorder. Let it be supposed for example that there is a tolerance of thispower of ±1 dB.

It will be recalled that the attenuation of the power of a transmittedelectromagnetic wave is subject to a law of decrease proportional to thesquare of the distance from emission.

In the example shown in the drawing, the computer 8, and hence as aresult the internal antenna 12, is disposed in the left portion of theinstrument panel of the vehicle 2. The external antenna 14 is alsodisposed at the instrument panel of this vehicle but in the rightportion of the latter. It is important in this case that neither ofthese two antennas be substantially equidistant from the four wheels 4or from the associated sensors. In this case, the two antennas 12, 14are disposed in the front of the vehicle. The process describedhereafter would operate in a similar manner if the two antennas werelocated at the rear of the vehicle, on the right side or on the leftside of the latter. For purposes of clarity, the description whichfollows will be given only with reference to the accompanying drawing,without taking account of the other possible positions of the antennas12 and 14.

Three successive steps are proposed to permit the location of thesensors 100, 101, 110, 111. In a first step, the front and rear sensorsare located. In the following step, the front right sensor isdistinguished from the front left sensor, and in the third final step itis proposed to distinguish the rear right sensor from the rear leftsensor. A preferred modified embodiment of the process according to theinvention is described hereafter.

First of all, a power balance of the four sensors is carried out. Thereceiver 6 is thus adjusted to maximum sensitivity with the internalantenna 12 and then the external antenna 14. The field level received isthus analyzed and memorized. The table below gathers the results of thepower balance carried out. TABLE 1 Internal antenna External antenna 1214 Identifying Reception (RSSI Reception (RSSI Sensor level) level) 100A0 B0 101 A1 B1 110 A2 B2 111 A3 B3

Ai and Bi, i=0 to 3, correspond to the power level for each signalreceived. This table, or at least the values it contains, is stored inthe memory of the computer 8.

The gain control of the receiver 6 is then adjusted to a gain value atwhich the internal and external antennas 12 and 14 receive the signalsemitted by the front sensors 100, 101 but do not receive the signalsfrom the rear sensors 110, 111. The power levels of the received signalsare collected in the following table. TABLE 2 Internal antenna Externalantenna 12 14 Identifying Reception (RSSI Reception (RSSI Sensor level)level) 100 C0 D0 101 C1 D1 110 (C2) (D2) 111 (C3) (D3)

The levels Ci, Di, i=0 to 3 correspond to the power level of the fieldcorresponding to the signal received by the receiver. The values C2, C3,D2, D3 are given in parentheses to indicate that they correspond to asignal that is not received or at least not detected, by the receiver 6.The results gathered in this table are also memorized in the computer 8.

There are thus detected the sensors which are disposed at the front ofthe vehicle and those disposed at the rear of the vehicle. It is clearthat the sensors disposed at the front of the vehicle are those forwhich a signal has been detected during measurement with reducedsensitivity.

However, the measurement results contained in the above tables show thatwe can locate not only the sensors mounted at the front and at the rearof the vehicle, but also can differentiate between the right sensors andthe left sensors by analyzing the values Ai, Bi, Ci and Di that aremeasured.

By analyzing the levels of the received signals, it is thustheoretically possible to locate the sensors. Thus, for a given antenna,the signal received at the level of the higher field will correspond tothe signal emitted by the sensor nearer the antenna. The measurementsmade with the two antennas permit correlating the obtained results.However, the obtained results are not always satisfactory because it isoften difficult particularly for sensors spaced from the antennas, todistinguish the attenuated signals, which is to say coming from arelatively remote sensor, and relatively faint. There are provided, asindicated above, the three steps to carry out the location.

The first step consists in carrying out the measurements collected inthe two above tables. There is thus obtained the distribution betweenthe front sensors 100, 101 and the rear sensors 110, 111.

The second step thus consists in distinguishing the front left sensor100 from the front right sensor 101. It will be seen that the distancebetween the sensor 100 mounted in the left front wheel and the internalreceiving antenna 12 implanted in the computer 8, is relatively smallrelative to the distance between this internal antenna 12 and the sensor101 mounted in the right front wheel. Similarly, the distance betweenthe sensor 101 mounted in the right front wheel and the external antenna14 is relatively small relative to the distance between this externalantenna 14 and the sensor 100 mounted in the left front wheel.

To distinguish between these two sensors, for example there is first ofall activated the internal antenna 12. The sensitivity of the receiver 6is thus decreased such that the signals emitted by the sensor 101mounted in the front right wheel will be weakly received, whilst thepower of the signals received by the sensor 100 mounted in the frontleft wheel is substantially greater. The analysis of the power levels ofthe fields corresponding to the received signals permits establishingfairly easily the position of each sensor (100 and 101). A measurementcarried out with a single antenna is sufficient, but it is preferable tomake a correlation by using the two antennas.

Thus, in the example given in Table 2, if C0<<C1 and D1<<D0, thecomputer 11 deduces from this that the sensor 100 is disposed to theleft front and that the sensor 100 is disposed to the right front.

We should also distinguish the right rear wheel from the left rearwheel. As for the front wheels, it is seen that the distance between thesensor 110 mounted in the left rear wheel and the internal antenna 12implanted in the computer 8, is less than the distance between thesensor 111 implanted in the right rear wheel and this same antenna.Similarly, for the external antenna 14, it is nearer the right rearwheel and hence the sensor 111, than the left rear wheel and hence thesensor 110. By thus activating the internal antenna 12, the externalantenna 14 being inactivated, when the sensitivity of the receiver 6 isnominal or decreased, the sensor 110 mounted in the left rear wheel isreceived with a greater power than from the sensor 111 mounted in theright rear wheel. Conversely, with the external antenna 14 activated andthe internal antenna 12 inactivated, the sensor 111 mounted in the rearright wheel is received with a greater power than the sensor 110 mountedin the left rear wheel. Thus we have in Table 1, A2<<A3 and B3<<B2.Similarly, in Table 2, C2<<C3 and D3<<D2. From this it can be concludedthat the sensor 110 is mounted at the left rear whilst the sensor 111 ismounted at the right rear.

To confirm the information as to location of the sensors 100, 101, 110,111 mounted on the wheels 4 of the vehicle 2, the process describedabove can be carried out several times successively. There can thus becarried out a statistical analysis of the obtained results. This permitsfreedom from uncertainty connected to the use of the technology of RFsignal emission. This statistical analysis can be carried out for thelocation of the four sensors of else only for the location of the rearsensors which are farthest from the antennas and hence for which theuncertainty of measurement is the greatest.

The present invention is not limited to the processes described above byway of non-limiting example nor to the system described for practicingthese processes. It also comprises all the modified embodiments withinthe scope of those skilled in the art within the range of those skilledin the art within the scope of the following claims.

Thus, to analyze the power of the received signals, instead of measuringthe power of a received signal, one can also act on the sensitivity ofthe receiver. One can for example depart from the nominal sensitivity ofthis receiver. The signals emitted by the four sensors are thus receivedby the receiver. By progressively decreasing this sensitivity, insteadof receiving the signals from the four sensors, there will no longer beobtained but the signals from the three sensors, then from two and thenfrom a single one. We can thus deduce that the first sensor whosesignals are not received is the sensor farthest from the antenna inquestion, and that the sensor whose signal is received even though thesensitivity is very low, is the sensor nearest the antenna in question.There can thus be deduced the position of the four sensors.

1. Process for locating sensors (100, 101, 110, 111) mounted each on onewheel (4) of a vehicle, each sensor being provided with an emitter andthe vehicle (2) being provided with a corresponding receiver (6) adaptedto receive signals emitted by each sensor (100, 101, 110, 111),characterized in that the receiver (6) is provided with an antenna (12),so disposed that it is not located substantially equidistant from anytwo sensors (100, 101, 110, 111), and in that the location of thesensors (100, 101, 110, 111) is carried out by analyzing the field powerreceived by the receiver (6) by means of the antenna (12) for eachsensor, the power of the field received by the antenna being greater,the nearer to the detector is the sensor that emitted the correspondingsignal.
 2. Process for locating sensors (100, 101, 110, 111) eachmounted on a vehicle wheel (4), each sensor being provided with anemitter and the vehicle (2) being provided with a corresponding receiver(6) adapted to receive the signals emitted by each sensor (100, 101,110, 111), characterized in that the receiver (6) is provided with twoseparate antennas (12, 14), separated from each other and disposed suchthat neither antenna is located substantially equidistantly from thesensors (100, 101, 110, 111), the two antennas (12, 14) being located onthe same side of the vehicle, and in that the location of the sensors(100, 101, 110, 111) is carried out by analyzing the field powerreceived by the receiver (6) by means of each antenna (12, 14) for eachsensor, the power of the field received by one antenna being thegreater, the nearer to the antenna is the sensor that emitted thecorresponding signal.
 3. Process for location according to claim 2 for avehicle having four wheels (4), characterized in that it comprises thefollowing steps: a) analysis of the power of the signals received by thetwo antennas (12, 14) so as to distinguish the two sensors (100, 101)located on the side of the antennas from the other two sensors (110,111), the signals received from these two sensors being the lessattenuated, b) one antenna being inactivated and the other beingactivated, analysis of the power of the signals received by the twosensors (100, 101) located on the same side as the antennas so as todetermine which sensor is the nearer the antenna that is stillactivated, c) one antenna being inactivated and the other beingactivated, analysis of the power of the signals received from the twosensors (110, 111) located on the side opposite the antennas (12, 14) soas to determine which sensor is nearer to the antenna that is stillactivated.
 4. Process for location according to claim 3, characterizedin that step a) is carried out as follows: adjustment of the receiver(6) to a predetermined sensitivity to receive all the signals emitted bythe four sensors (100, 101, 110, 111) with the two antennas (12, 14),and adjustment of the receiver (6) to a lesser sensitivity such that,for the two antennas (12, 14), the signals emitted by the sensors (100,101) located on the same side as the antennas will be received whilstthe signals emitted by the other sensors (110, 111) are not received. 5.Process for location according to claim 3, characterized in that in stepb) and/or step c), the power analysis is carried out by adjusting thesensitivity of the receiver (6) such that the signal power received bythe sensor to be identified and located near the inactive antenna willbe weak, whilst the power of the signal received by the sensor to beidentified and located near the active antenna will be substantiallystronger, and in that the analysis of the power levels received is madeso as to detect the position of the two sensors whose signals areanalyzed.
 6. Process for location according to claim 3, characterized inthat in step b) and/or step c), the power analysis is carried out bydecreasing the sensitivity of the receiver (6) until a single signalemitted by the sensors to be identified will still be received by thereceiver (6), and in that a determination of the position of the twosensors to be identified is thus carried out.
 7. Process for locationaccording to claim 3, characterized in that step b) and/or c) is carriedout twice in succession, once with the first antenna active and thesecond antenna inactive and the second time with the first antennainactive and the second antenna active, and in that a step ofcorrelation is provided to compare the results obtained in the course ofthese two analyses.
 8. Process for location according to claim 3,characterized in that step c) is carried out several times in arepetitive manner and in that a statistical analysis of the results iscarried out.
 9. Process for location according to claim 2, characterizedin that the two antennas (12, 14) are integrated into the instrumentpanel of a vehicle, one antenna being located in the right portion andthe other in the left portion of this instrument panel.
 10. Process forlocation according to claim 9, characterized in that one antenna (12) isintegrated into an electronic housing integrating the receiver (6)whilst the other antenna (14) is an antenna external to this housing.11. Process for location according to claim 1, characterized in that itis carried out several times in a repetitive manner and in that astatistical analysis of the results is carried out.
 12. Device forlocation to practice a process according to claim 2, characterized inthat it comprises a receiver (6), two antennas (12, 14), a switch withtwo inputs insulated from each other and one output, mounted such thatthe receiver (6) is connected to one or the other of the antennas, aswell as a computer (8) for the control and management of the device. 13.Device for location according to claim 12, characterized in that thereceiver (6) is integrated into the computer (8).
 14. Device forlocation according to claim 12, characterized in that one antenna (12)is integrated into the computer (8) and in that the other antenna (14)is an external antenna.